Aromatic hydroxycarboxylic acids, particularly p-hydroxybenzoic acid, salicylic acid, 2-hydroxy-3-naphthoic acid, etc., have long been known for their usefulness as raw materials for the production of antiseptic and antifungal agents, pharmaceuticals, dyestuffs, pigments and the like, and in recent years, have furthermore acquired increasingly greater importance not only as starting compounds for the synthesis of agricultural chemicals, color developing agents for thermosensitive recording paper, etc. but also as monomers for aromatic polyesters.
These aromatic hydroxycarboxylic acids have conventionally been produced by means of the so-called Kolbe-Schmitt process involving a vapor-solid phase reaction of an alkali metal salt of aromatic hydroxy compound with carbon dioxide. Lately, one of the present inventors has improved the said vapor-solid phase reaction process into the liquid-solid phase reaction process making use of a suspension phase, and thus, there has been established a process which permits an industrial-scale, mass-production of such aromatic hydroxycarboxylic acids [refer to the specification of Patent Application No. 39281/1983 (Laid-Open Patent Publication No. 164751/1984)].